1. Field of the Invention
The present invention relates to an exposure apparatus and a device fabrication method.
2. Description of the Related Art
An exposure apparatus which projects (reduction projection) and transfers the pattern of a reticle onto a substrate coated with a resist (photosensitive agent) is employed to fabricate a fine semiconductor device such as an LSI or a VLSI. As the packing density of a semiconductor device increases, a demand has arisen for further pattern miniaturization. The resolution of an exposure apparatus improves along with the development of a resist process.
As a technique of improving the resolution of an exposure apparatus, the so-called immersion method in which the space between a substrate and the final surface (final lens) of a projection optical system is filled with a liquid is available. For example, the resolution of an exposure apparatus when the space between a substrate and the final surface of a projection optical system is filled with pure water (Refractive Index=1.44) becomes 1.44 times that when the space between the substrate and the final surface of the projection optical system is filled with a gas (air). This amounts to increasing the numerical aperture (NA) of the projection optical system to 1.44 times. With the immersion method, a resolution equivalent to an NA of 1 or more that is impossible in the conventional method can be obtained.
Roughly two methods of filling the space between the substrate and the final surface of the projection optical system with a liquid are available. In the first method, the entire substrate and the final surface of the projection optical system are accommodated in a liquid tank. The second method is the local fill method in which a liquid is supplied only to the space between the substrate and the final surface of the projection optical system.
In the immersion method, it is necessary to maintain the liquid that fills the space between the substrate and the final surface of the projection optical system at a predetermined temperature. It is also necessary to suppress cooling due to heat of vaporization generated as the liquid that fills the space between the substrate and the final surface of the projection optical system vaporizes. To meet these requirements, Japanese Patent Laid-Open Nos. 2005-252247 and 2006-054468 propose, for example, an exposure apparatus equipped with a temperature control system which controls the temperature of a member that comes into contact with the liquid, and an exposure apparatus including a substrate stage equipped with a heater.
In an exposure apparatus which adopts the local fill method, a liquid that fills the space between a substrate and the final surface of a projection optical system is recovered while the liquid is mixed with a gas (gas-liquid mixture state). In this manner, when the liquid is recovered in a gas-liquid mixture state, vaporization of the liquid is promoted, leading to a considerable decrease in temperature of a liquid recovery path. The decrease in temperature of the liquid recovery path adversely affects members arranged around the liquid recovery path, such as the projection optical system and measuring system, thus degrading the pattern transfer accuracy.